The liberal democrats are too mainstream to actually say they would legalise weed, but if you read between the lines ... cannabis would be legalised at least by the end of a lib dem government.

The greens want to legalise the weed but not anything else. I think some members of the lib dems, and even some who are quite high up, would want to legalise all drugs. If you look beyond the surface and see what some of them have said in the 1970's etc that is, and assume that they haven't really changed their views since.

The only party that would actually legalise all drugs is LPUK, but you might not like them because they're economically right-wing.